qemu-file: Fix qemu_put_compression_data flaw

Current qemu_put_compression_data can only work with no writable
QEMUFile, and can't work with the writable QEMUFile. But it does
not provide any measure to prevent users from using it with a
writable QEMUFile.

We should fix this flaw to make it works with writable QEMUFile.

Signed-off-by: Liang Li <liang.z.li@intel.com>
Suggested-by: Juan Quintela <quintela@redhat.com>
Message-Id: <1462433579-13691-5-git-send-email-liang.z.li@intel.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>

migration/qemu-file.c

@@ -615,8 +615,14 @@ uint64_t qemu_get_be64(QEMUFile *f)
     return v;
 }
 
-/* compress size bytes of data start at p with specific compression
+/* Compress size bytes of data start at p with specific compression
  * level and store the compressed data to the buffer of f.
+ *
+ * When f is not writable, return -1 if f has no space to save the
+ * compressed data.
+ * When f is wirtable and it has no space to save the compressed data,
+ * do fflush first, if f still has no space to save the compressed
+ * data, return -1.
  */
 
 ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
@@ -625,7 +631,14 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
     ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
 
     if (blen < compressBound(size)) {
-        return 0;
+        if (!qemu_file_is_writable(f)) {
+            return -1;
+        }
+        qemu_fflush(f);
+        blen = IO_BUF_SIZE - sizeof(int32_t);
+        if (blen < compressBound(size)) {
+            return -1;
+        }
     }
     if (compress2(f->buf + f->buf_index + sizeof(int32_t), (uLongf *)&blen,
                   (Bytef *)p, size, level) != Z_OK) {
@@ -633,7 +646,13 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
         return 0;
     }
     qemu_put_be32(f, blen);
+    if (f->ops->writev_buffer) {
+        add_to_iovec(f, f->buf + f->buf_index, blen);
+    }
     f->buf_index += blen;
+    if (f->buf_index == IO_BUF_SIZE) {
+        qemu_fflush(f);
+    }
     return blen + sizeof(int32_t);
 }
 

migration/ram.c

@@ -821,7 +821,13 @@ static int do_compress_ram_page(CompressParam *param)
                                   RAM_SAVE_FLAG_COMPRESS_PAGE);
     blen = qemu_put_compression_data(param->file, p, TARGET_PAGE_SIZE,
                                      migrate_compress_level());
-    bytes_sent += blen;
+    if (blen < 0) {
+        bytes_sent = 0;
+        qemu_file_set_error(migrate_get_current()->to_dst_file, blen);
+        error_report("compressed data failed!");
+    } else {
+        bytes_sent += blen;
+    }
 
     return bytes_sent;
 }
@@ -965,10 +971,12 @@ static int ram_save_compressed_page(QEMUFile *f, PageSearchStatus *pss,
                  * first page is sent out before other pages
                  */
                 bytes_xmit = do_compress_ram_page(&comp_param[0]);
-                acct_info.norm_pages++;
-                qemu_put_qemu_file(f, comp_param[0].file);
-                *bytes_transferred += bytes_xmit;
-                pages = 1;
+                if (bytes_xmit > 0) {
+                    acct_info.norm_pages++;
+                    qemu_put_qemu_file(f, comp_param[0].file);
+                    *bytes_transferred += bytes_xmit;
+                    pages = 1;
+                }
             }
         } else {
             pages = save_zero_page(f, block, offset, p, bytes_transferred);